Emulsion explosives have become an increasingly important product offering in commercial mining, quarrying and construction as well as providing potential benefits to the military. A significant quality issue in this area of technology is maintenance of performance of the compositions over extended periods of time.
Explosives, propellants and munitions often are stored for extended periods of time under a wide variety of conditions, e.g., temperature, humidity, etc. Performance of the emulsions can be adversely affected if precautions are not taken to insure stability of the emulsion. Moreover, higher performance materials often require the addition of solid materials such as aluminum metal or glass to the basic emulsion. These materials tend to add further internal stress to the emulsion.
Improved surfactants and coating agents have led to improved shelf life, but the issue has not been satisfactorily resolved in all cases, especially in the case of high performance compositions. Accordingly, the industry is continuing to search for ways to improves emulsion stability.
Water-in-oil emulsions typically comprise a continuous organic phase and a discontinuous aqueous phase. Energetic emulsion compositions such as explosive emulsions and propellant emulsions contain water and an oxygen-supplying source such as ammonium nitrate in the aqueous phase, the aqueous phase being dispersed throughout the continuous organic phase which comprises an organic fuel. Energetic emulsion compositions, for example explosive emulsions, are known to those skilled in the art. Cap-sensitive explosive emulsions are water-in-oil explosive emulsions which can be detonated without the use of a booster. Such emulsion explosives are also known to those skilled in the art. Propellant emulsions such as rocket propellants are also known.
U.S. Pat. No. 3,130,096 discloses a propellant composition in which a mixture of diglycidyl ethers is cured to form a binder which is admixed with an oxidizer material. The binder also functions as a fuel.
U.S. Pat. No. 3,177,101 discloses a gas-generating composition proposed by mixing a carboxyl terminated liquid polyester with ammonium nitrate powder and a curing agent. The curing agent reacts with the carboxyl portion of the liquid polyester, and the material sets to a solid consistency. The patent distinguishes between gas-generating compositions, propellants, and explosives by noting that gas-generating compositions have a substantially lower burning rate than conventional propellants, just as propellants have a substantially lower burning rate than explosives.
U.S. Pat. No. 3,790,416 discloses a composite propellant composition in which dewetting of the propellant composition under applied stress is substantially reduced. Reduced dewetting is achieved through the use of poly-functional amines which are capable of forming a chemical bond between the oxidizer (oxygen-containing ammonium salt) and the binder in the cured propellant. The composite propellant composition comprises oxidizers and optionally fuels in the form of small solid particles uniformly distributed in a polymeric binder.
U.S. Pat. No. 4,104,092 discloses gelled explosive compositions which are sensitized with water-in-oil explosive emulsions. The gelled explosive compositions basically comprise an aqueous solution of oxidizers, fuels and sensitizing agents which have been gelled with one or a variety of aqueous gelling agents such as guar gum and a suitable cross-linker. The patented compositions are distinguished from water-in-oil emulsion explosives in that emulsion explosives are comprised of two distinct phases, the carbonaceous oil being the continuous phase and the aqueous solution of the oxidizing agents being the discontinuous phase of the emulsion.
U.S. Pat. No. 4,216,040 discloses an inverted phase or water-in-oil blasting composition having a water-immiscible liquid organic fuel as a continuous phase, an emulsified aqueous inorganic oxidizer salt solution as a discontinuous phase, and an organic cationic emulsifier having a hydrophilic portion and a lipophilic portion, wherein the lipophilic portion is an unsaturated hydrocarbon chain. Thickening and cross-linking agents are not necessary for stability and water-resistancy. However, such agents can be added if desired. The aqueous solution of the composition can be rendered viscous by the addition of one or more thickening agents of the type and in the amount commonly employed in the art. Such thickening agents include galactomannin (preferably guar gums); guar gum of reduced molecular weight, biopolymer gums, polyacrylamide and analogous synthetic thickeners, flours, and starches. Cross-linking agents for cross-linking the thickening agents also are well known in the art. Such agents are usually added in trace amounts and usually comprise metal ions such as dichromate or antimony ions. The liquid organic, which forms the continuous phase of the composition, also can be thickened, if desired, by use of a thickening agent which functions in an organic liquid.
U.S. Pat. No. 4,343,663 discloses self-supporting, water-bearing explosive products which contain discreet cells of an aqueous solution of an inorganic oxidizing salt and/or an amine salt encapsulated by a cross-linked (thermoset) resin matrix.
U.S. Pat. No. 4,420,349 describes a two-component emulsion explosive composition consisting of a continuous oil/fuel phase and a discontinuous oxidizer salt phase and, as an emulsifier, a dimer acid glyceride wherein the dimer acid has a carbon chain length of C18-C60. The composition is said to demonstrate superior properties of long period storage stability and sensitivity.
U.S. Pat. No. 4,473,418 discloses an emulsion explosive composition which may include thickening and/or cross-linking agents. The typical thickening agents include natural gums, such as guar gum or derivatives thereof, and synthetic polymers, particularly those derived from acrylamide. Water-insoluble polymeric or elastomeric materials, such as natural rubber and synthetic rubber, may be incorporated into the oil phase. The cross-linking agents are not further specified.
U.S. Pat. No. 4,525,225 discloses a solid water-in-oil emulsion explosive comprising a discontinuous emulsion phase formed of an aqueous solution of an oxidizer salt and a continuous emulsion phase formed of a solid carbonaceous fuel derived from an oleaginous liquid.
U.S. Pat. No. 4,708,753 discloses that emulsion explosives may contain water phase or hydrocarbon phase thickeners such as guar gum, polyacrylamide, carboxymethyl or ethyl cellulose, biopolymers, starches, elastomeric materials and the like as well as cross-linkers for the thickeners, such as potassium pyroantimonate and the like.
U.S. Pat. No. 4,822,433 discloses an explosive emulsion composition comprising a discontinuous phase containing an oxygen-supplying component and an organic medium forming a continuous phase wherein the oxygen-supplying component and organic medium are capable of forming an emulsion which, in the absence of a supplementary adjuvant, exhibits an electrical conductivity measured at 60° C., not exceeding 60,000 picomhos/meter. The conductivity may be achieved by the inclusion of a modifier which also functions as an emulsifier.
U.S. Pat. No. 4,936,932 relates to an explosive emulsion composition comprising a discontinuous oxidizer phase and a continuous fuel phase comprising an aromatic hydrocarbon compound. The composition essentially contains as the emulsifying agent a polyisobutylene succinic anhydride based compound in admixture with 1-4 sorbitan and oleic acid. The composition is said to demonstrate high explosive strength and excellent stability.
U.S. Pat. No. 5,244,475 discloses an emulsion composition with a polymerizing and/or cross-linking agent and method for its use in improving the manufacturing, packaging, transporting, storage placement and blasting characteristics of explosives containing an emulsion. More specifically, compositions and methods directed to controlling the rheology of an emulsion or explosive containing an emulsion by polymerizing and/or cross-linking the continuous phase of the emulsion by employing hydroxy-terminated polybutadiene and polymerization agents and/or maleic anhydride adducted polybutadiene and cross-linking agents, but without compromising the integrity of the explosive reaction.
U.S. Pat. No. 5,401,341 relates to a water in oil emulsion explosive containing an oxidizing material in the discontinuous water phase, and the continuous oil phase acts as a carbonaceous fuel. The patent relates to such explosives in which polyfunctional carboxylic acids, sulfonic acids, or phosphorous-containing acids, soluble in the oil phase are caused to cross-link using an inorganic cross-linker, thereby causing the viscosity of the emulsion to increase.
U.S. Pat. No. 5,936,194 describes thickened emulsion compositions comprising a discontinuous oxidizer phase, continuous fuel phase, an emulsifier and a thickener composition comprising a carboxy-containing polymer and a promoter selected from the group consisting of sodium thiocyanate and thiourea.
European Patent application EP 561,600 A discloses a water-in-oil emulsion explosive in which the emulsifier is the reaction product of a substituted succinic acylating agent, having at least 1.3 succinic groups per equivalent weight of substituents, with ammonia and/or an amine. The substituent is a polyalkene having an number average molecular weight of greater than 500 and preferably 1300-1500.
It is an object of the present invention to provide a stabilized water in oil emulsion composition that can be stored for an extended period of time without undergoing deterioration that adversely affects performance.